Treatment of mice with various biologic response modifiers (BRM) results in increases in both the number and cytolytic activity of large granular lymphocytes (LGL) in the liver and spleen. Similarly, injection of specific cytokines, or combinations of cytokines, can mediate the recruitment of different populations of leukocytes into tissue sites. Thus, cytokines or other mediators released in these organs following BRM treatment may be responsible for the recruitment and/or activation of LGL observed. The mechanism by which these cells accumulate is being studied in vitro, using a modified Boyden chamber chemotaxis assay and collagen-coated, millipore filters. Using this technique, we have examined the release of chemotactic activity for LGL from liver cell cultures treated in vitro with BRM. Although the BRM themselves did not stimulate LGL migration, treatment of isolated cells induced the production and release of soluble factors that were chemotactic for LGL in vitro. Since these BRM are known to induce the release of a number of cytokines from immune cells which may be important in recruiting LGL in vivo, we have studied the chemotactic activity of these agents for LGL in vitro. We have determined that several different cytokines can induce chemotaxis of LGL, including partially purified rat interferon alpha/beta (IFN-alpha/beta), recombinant human (rh) interleukin 2 (IL-2), rhIL-6, and rh tumor necrosis factor alpha (TNFalpha). These cytokines stimulated chemotaxis of LGL in a dose and time-dependent manner, suggesting that local release of these agents may contribute to the recruitment of LGL and other leukocytes in vivo. Future studies are focused on the characterization and identification of the chemotactic factors released from isolated liver cells. Using the peritoneal cavity as a model, we have also begun to study the mechanisms by which other leukocyte types recognize and respond to stimuli in vivo. These studies will allow us to determine the role of cytokines in the recruitment of different populations of leukocytes during an inflammatory response.